!)8 University of California Publications in Geological Sciences 



Verdi rocks do not represent the Truckee as described by King. It is pertinent that 

 King (1878, vol. 2, p. 849) originally noted that the Verdi beds are quite unlike 

 the Truckee lithologically. They appeared on the Atlas of the Fortieth Parallel as 

 Truckee chiefly because they are tilted to about the same degree, and were there- 

 fore thought to be of approximately the same age, and Truckee then being con- 

 sidered Miocene on the basis of limited fossil evidence (King, 1878, vol. 1, p. 423). 



Not only are there marked difference between the Truckee formation and the 

 sediments at Verdi which have previously been referred to the Truckee, but their 

 relations to older rocks also differ greatly. The Truckee formation, as exposed over 

 a wide area in the Carson Sink basin, includes three members: (1) a lower basalt 

 breccia and tuff which grades upward into a sedimentary basalt breccia, coarse 

 gritty sandstone, coquina, and a few thin beds of diatomite ; (2) a thick, relatively 

 pure diatomite section with numerous pumice beds and a few thin (2- to 3-inch) 

 sandstones; and (3) an upper flaggy limestone-pebble conglomerate-sandstone-thin 

 diatomite member (Axelrod, 1956, p. 99). The type Truckee grades downward into 

 siliceous shales of the Desert Peak formation, which in turn rests on basalt and 

 biotite andesite of the Chloropagus formation. By contrast, the Verdi elastics are 

 preponderantly andesitic, derived chiefly from erosion of the Oligocene Alta and 

 the Mio-Pliocene Kate Peak andesite, on which the sediments rest unconformably. 

 Associated with the coarse conglomerates and sandstones in the lower part of the 

 section are a few thin Kate Peak breccias ; in the nearby area the Verdi sediments 

 are interbedded with the upper part of the Kate Peak andesite. Since the fluvio- 

 lacustrine Verdi section differs greatly from the Truckee, it must represent a dif- 

 ferent formation. 



During my studies of the geologic occurrence of several Late Tertiary floras in 

 western Nevada, sediments similar to those exposed near Verdi have been recog- 

 nized over a wide region, extending from the Verdi area 75 miles southeastward 

 to the middle drainage of the East Walker River, and 40 miles eastward to the 

 margins of the Carson Sink. This fluvio-lacustrine section represents the Coal 

 Valley formation, whose type area is at Coal Valley 4 miles south of Morgan's 

 Ranch (Hawthorne Quadrangle), where the formation is 3,900 feet thick (Axelrod, 

 1956, p. 29) . There, as elsewhere, the section is characterized by clasts derived from 

 erosion of the Late Tertiary Sierran andesites. The section is typically fluvio- 

 lacustrine, the andesitic sandstones and conglomerates alternating with tuffaceous 

 shale, diatomite, soft lake clays, and locally with lignitic beds. Lenses of Kate Peak 

 andesite are interbedded in its basal part at Coal Valley, and also at other localities 

 in western Nevada, as in the hills near Churchill north of Yerington, in the Desert 

 Creek Range, and at Chalk Hills north of Virginia City. These conformable rela- 

 tions are not found in the Verdi basin because Kate Peak andesite was deformed 

 in this area (and to the west) during the closing phases of vulcanism, resulting in 

 the unconformable relation. Nonetheless, a few, thin hornblende andesite tuffs and 

 breccias occur in the lower part of the section, showing that eruptions continued 

 in the Verdi region into the early phases of Coal Valley deposition. 



The Coal Valley is closely related to the Mehrten formation on the lower west 

 slope of the Sierra Nevada. The chief difference is that the Coal Valley represents 

 a fluvio-lacustrine section, whereas lake beds make up only a very minor part of 



